Thread-cutting tap



July 31, 1928. 1,679,234

0. A. A. TENOW THREAD CUT'I I NG TAP Filed Aug. 13, 1926 jun 6721 071 Patented July 31, 1928.

UNITED STATES PATENT OFFICE.

OLOF A. A. TENOW, OF CHICAGO, ILLINOIS, ASSIGNOR OF ONE-HALF T JUST'US 1P.

SEEIBUIRG.

THREAD-CUTTIN G TAP.

Application filed August 13, 1926. Serial No. 128,976.

As a preface to a description of my invention, it may be stated that as taps have hitherto been constructed the forming thereby of accurate threads is practically impos- 5 sible due to outward deflection of the cutt ng edge portions of the tap in encounterlng relatively hard, and therefore h1ghly resistant, portions of the metal of the ob ect, being tapped and which commonly exist,

particularly in iron and steel, owlng to the non-homogeneous character thereof. The cutting portions of the tap being sub ected to non-uniform resistance during the cutting operation, the thread produced thereby 1s caused to be deeper adjacent the harder portions of the metal and is thus rendered nonuniform and inaccurate, with the manifest disadvantages.

My object is to providea construction of tap by the use of which the. ob ections above pointed out will be avoided and accurate threads be produced.

Referring to the accompanying drawmg l5 Figure 1 is a view in side elevation: of a tap comprising one embodiment of my invention. Figure 2 is a section taken at the line 2 on Fig. 1 and viewed in the direction of the arrow; and Figure 3, a cross-sectlonal 0 view of still another embodiment of the 1nvention, the section being talien at a line corresponding with line 2 on F 1g. 1,

Referring first to the construction llustrated in Figs. 1 and 2, the tap comprises a 5 body portion threaded, as represented at'. l0, with the extremity of its cutting-end portion tapered, generally as shown and as in the case of taps of common form. The tap 1s centrally longitudinally apertured, throughout its lengt as represented at 11 and 1s slotted longitudinally, as represented at 12, preferably throughout the length of the threaded portion of the body, this slot opening through the extremity of the cutt ng i end portion of the latter. The s de portion of the body opposite the slot 12 18 cut away at 13, from a point between the ends of the threads to the extremity of the cutting-end portion of the body preferably to cause the I tap to present substantially throughout the length of this cut-away portion, a contour substantially as shown (see Fig. 2). The cutting ed 'e portions of the tap are represented at 14, the tap in the forming of a thread being rotated in the direction of the arrow in Fig. 2.

The cross-sectional form of the such, as shown, that .when the cutting edge portion 14 encounters, in the cutting o eration, a relatively hard portion of the .o ject being threaded, that portion of the tap at one side of the slot 12 and which is equipped with the cutting edge, yields to the left in Fig. 2 and thus the cutting edge swings inwardly in a direction away from the surface being cut and gouging of the surface being out is avoided. As the surface being cut is operated on successively by the cutting edges of the tap, engagement of its cutting edges with such relatively hard portions of the object, which deform the tap as stated, to accurately thread these portions of the object, so that such threaded depth and contour as the other portions of the thread, whereby'a uniform thread will be produced in the object.

Referring to the construction shown by a cross-sectional View in Fi 3, this constitutes another form oftap of t e slotted t pe and provides a cutting edge of a highly esirable angular shape. This construction, the cutting edge of which is represented at 27, is the same as that of Figs. 1 and 2, except that the tap is not centrally apertured; the slot,

represented at and corresponding with the slot 12, is deeper than the latter; and the cut-away portion 26 corresponding wit-h the cut-away portion 13 is narrower.

It will be understood that when the cutting edge 27 encounters. a relatively hard portion of the object bein threaded, the part of the tap at one side 0% the slot 25 and carrying the cutting edge portion, will deform to the left in Fig. 3 permitting the cutting edge portion to move inwardly toward the tap will operate by successive tap is i portions will be of the same the axis of the tap, an accurate and uniform thread being produced in the object by reason of the subjection of the latter to successive cutting actions during the rotation of the tap.

It will be understood as to both of the constructions shown the cutting edge portion of the tap is never causedto ouge into the surface being threaded either because of the deformation or yielding of the body portion of the tap in a direction to. project the cutting edge toward the surface being 'stituting embodiments of my invention, I do not wish to be understood as intending to limit m invention thereto as it may be embodied in other forms of construction without departing from the spirit of my invention. 1

What I claim as new, and desire to secure by Letters Patent, is:

1. A thread-cutting tap having a threadcutting portion with a portion thereof at one side of its axis extending lengthwise of the tap cut away to provide cutting edges, said tap being slotted lengthwise thereof at the other side of its axis, with the slot so disposed that the cutting edge portions of the tap move toward the axis thereof when encountering the resistance of relatively hard portions of the work.

2. A-thread-cutting tap having a threadcutting ortion with a portion thereof extending engthwise of the tap cut away to provide cutting edges, said tap containing a slot extending in the direction of the length of the tap and opening through a side of the tap opposite that at which said cutting edges extend and of such depth that, in the flexing of the cutting-edge-equipped portion of the tap in encountering relatively hard portions of the work, the fiexure occurs elsewhere than at the side of the axis of the tap opposite that at which said cutting portions are located.

3. A thread-cutting tap having a threadcutting portion with a portion thereof extending lengthwise of the tap cut away to provide cutting edges, said tap containing a slot extending in the direction of the length of the tap and opening through a side of the tap opposite that at which said cutting ed es extend and of such depth that, in the flexing of the cutting-edge-e uipped portion of the tap in encountering re atively ard ortions of the work, the flexure occurs elsew ere than at the side of the axis of the tap opposite that at which said cutting portIOIIS are located, said Slot at its inner extremity being of enlarged width.

4 A thread-cutting tap having a threadcutting ortion with a portion thereof extend ng engthwise of the tap cut away to provide cutting edges, said tap containing a slot extending in the direction of the length of the tap and opening through a side of the tap opposite that at which said cutting edges extend and of such depth that, in the flexing of the cutting-edgc-equipped portion of the tap in encountering relatively hard portions of the work, the flexure occurs el'-'cwhere than at the side of the axis of the tap opposite that at which said cutting portions are located, said slot at its inner extremlty being of enlarged width and of curved form in cross section.

5. A thread-cutting tap having a threadcutting portion with a portion thereof extending lengthwise of the tap cut away to provide cutting ed es, said tap containing a slot extending in the direction of the length of the tap and opening through a side of the tap opposite that it which said cutting edges extend and of such depth that, in the flexing of the cutting-edge-equipped portion of the tap in encountering relatively hard portions of the work, the fiexure occurs el'ewhere than at the side of the axis of the tap opposite that at which said cutting portlons are located, said slot at its inner extremity being of enlarged width and of curved form in cross section and the outer surface of the tap at said curved portion of said slot being curved generally in conformance with the curved wall of said slot.

OLOF A. A. TENOW. 

